Servo assisted operating mechanism



Jan. 5, 1954 Filed Aug. 15, 1950 S. H. EDGE SERVO ASSISTED OPERATING MECHANISM 5 Shee ts-Sheet 1 I nvenior A fforn eys Jan. 5, 1954 s. H. EDGE 2,664,707

SERVO ASSISTED OPERATING MECHANISM Filed Aug. 15, 1950 3 Sheets-Sheet 2 Inventor mhww mim

Attorneys Jan. 5, 1954 s. H. EDGE 2,654,707

SERVO ASSISTED OPERATING MECHANISM Filed Aug. 15, 1950 3 Sheets-Sheet 5 Inventor Attorneys Patented Jan. 5, 1954 SERVO ASSISTED OPERATING MECHANISM Stanley Howard Edge, Lincoln, England, assignor to Clayton Dewandre Company Limited, Lincoln, England Application August 15, 1950, SerialNo. 179520 1 Claim.

This invention relates to servo-assisted operating mechanism and has more particular reference to mechanism of the kind employed for actuating the brakes of an automobil vehicle,

the object of the invention being to provide an improved construction or arrangement capable of installation as a self-contained unit and designed for boosting a hydraulic transmission system while enabling emergency operation of the hydraulic system to be effected in the event of failure of the source of power. 7

According to the invention a servo-assisted operating mechanism includes a hydraulic transmission system between a pedal or like actuator and an output cylinder or cylinders, a hydraulic cylinder forming part of said transmission system, and a mechanical transmission arrangement operated by increase of pressure in the hydraulic cylinder to release a vacuum servo device for operation to reinforce or boost the impulse transmitted through the hydraulic system to a degree proportional to the pressure exerted on the actuator.

According to one form of the invention a servo assisted brake operating mechanism comprises hydraulic impulse transmission means between a master cylinder and a brake applying cylinder or cylinders, a mechanical transmission arrangement operated by pressure transmitted from the master cylinder to open a vacuum valve to operate a vacuum cylinder, means operated by said vacuumcylinder to actuate a valve member to shut off the hydraulic transmission from the master cylinder and thereafter transmit movement from the vacuum cylinder through the hydraulic system to the brak cylinder or cylinders to a degree proportional to the pressure applied to the pedal or other actuator.

Reference will now be made to the accompanying drawings which show a servo-assisted mechanism for operating vehicle brakes and in which:

Fig. 1 is a diagrammatic view showing the inoperative position,

Fig. 2 is a view similar to Fig. 1 showing an operative position, and

Fig. 3 is a sectional view of an alternative arrangement.

In the arrangement illustrated a servo-assisted mechanism applicable to the operation of vehicle brakes includes an actuating pedal l arranged to operate a hydraulic master cylinder 2 of known construction which is connected by a conduit 3 to an operating cylinder 4 in turn connected by a conduit 5 to separate cylinders arranged to actuate the vehicley'brakes. Within the operating cylinder .4 is slidably mounted a cylindrical valved piston 6 having at one end a coned valve seating 1 surrounding an'opening 8 and completely open at its opposite end. The valved piston i5 is movable, as hereinafter described, into an extension 9 of the cylinder 5. Between the outer end of the extension 9 and the inner surface of the end It of' the valve member is disposed a helical spring II which opposes operative movement of the valved piston and serves to return it to normal position after operation.

The cylindrical valved piston 6 is surrounded through the major portion of its length by an annular space l2 which is always in free communication with the'master cylinder 2. The valved piston 6 is slidable in an end portion 53 of the cylinder 4 and adjacent this end portion is disposed a sealing member [4, in this instance a cup Washer disposed in an annular chamber it to prevent displacement during operation of the valved piston, the said sealing member M serving to cut off communication between the annular space l2 and theconduit 5 leading to the output cylinders during operation of the mechanism.

Disposedin axial alignment with the valved piston 6 is a co-operating tapered valve member l6 adapted to enter the coned seating and formed, at the end of a piston rod ll passing through a sealed gland l8 and carrying the piston IQ of a vacuum cylinder 20.. This cylinder has an atmospheric port 2| atthe end remote from the valve member Hi and a spring 22 to return the piston 19 to th position shown in Fig. 1 after operation 1 At the end of the operating cylinder 4 adjacent theLvalve members 1 and I6 is an'annular shoulder 23 against which the end of the valved piston 6 abuts inits rest position and between this shoulder andthe gland I8 is a cylindrical chamber 24 to enablethe hydraulic fluid to act on the rear of the valved piston 6 at all times. Adjacent this point the annular space i 2 com.- municates through a port 25 with a cylinder 26 containing a plunger 21 whose head extends beyond the casing 28 wherein the operating cylinder 4 is formed and engages the edge of a lever 29. movable about a'pivot 30 carried by the said casing. The opposite end of the lever 29 is connected to a stem 3| depending into a chamber 32 formed in the casing 28 and provided with atmospheric ports 33.- The stem 3! carries at its lower end a cylindrical casing 34 whose exterior is connectedtothewalls'of the chamber 32 by a flexibleidiaphragm 35. The top of the casing 34 is provided with ports 3Band its base 37 has a central aperture which passes freely around a valve seating 33 within which is a passage 39 in permanent communication with a source of vacuum. Within the casing 36 is a disc valve member 40 normally held onto the seating 38 by a spring i-l whose upper end bears against the top of the casing 34 and which serves to close the vacuum passage 39. The casing 34 is normally held in the position shown in Fig. 1 by a spring 42 whose upper end bears against the top of the chamber 32 whose base communicates by an annular passage 43 and a passage id with the interior of the vacuum cylinder 26. In the rest position, shown in Fig. 1, therefore, the interior of the cylinder 20 is in communication with atmosphere through passage 53, casing 3d and chamber 32 the interiors of which are open to atmosphere through the ports 33.

The operation of the arrangement above described is as follows:

When effort is applied to the brake pedal l the hydraulic master cylinder 2 is operated tocreatepressure in the operating cylinder 4 which pressure causes movement of the plunger 3? to rock the lever 28 in an upward direction around its pivot 3!; and lift the cylindrical casing 3 1 to the position shown in Fig. 2. These operations first close communication between the cylinder 25 and atmosphere as the base ill of casing 35 engages the underside of the disc valve member iii! and thereafter lift the disc valve member to place the vacuum passage 35 in communication with the cylinder 25} by way of passages 3 and 34.

The piston i9 is accordingly moved towards the left (see Fig. 2) to cause the valve member I6 to engage in the valve seating I, close the end of the cylindrical valved member 6 which by con tinued movement of the piston 19 is pushed outwards against the resistance of the spring H to assist the hydraulic transmission of effort through the conduit 5 to the brake applying cylinders. The degree of vacuum exerted in the cylinder 2!? is proportional to the pressure applied to the pedal i up to a predetermined point, when full vacuum is exerted. This is achieved by pro portioning the flexible diaphragm 35 in relation to the diameter of the hydraulic plunger 21 and the leverage between the two exerted through the pivoted lever 29. After the initial movement has lifted the plunger 2? and stem ill, the opening of the disc valve member til places the whole of the interior of the chamber 32 below the diaphragm 35 under vacuum which, in conjunction with the springs 42 and 4 I tends to withdraw the diaphragm from the distened position shown in Fig. 2 to that shown in Fig. 1 and simultaneously to seat the disc valve member it. In consequence a sustained pedal effort is necessary to maintain the cylinder 28 under vacuum and an increasing eifort at the pedal to obtain a proportional increase in the elTort transmitted to the brake applying cylinders to obtain full braking of the vehicle.

In the alternative construction shown in Fig. 3, the extension 5 and valved piston 6 of the arrangement shown in Figs. 1 and 2 are replaced by a cylinder 25 into which is fitted a piston 46 provided with a cup washer ll. The inner end of the piston 46 is fixed into the casing 28 and terminates in the valve seating 1 adapted to be engaged as before by the valve member it which, when actuated, pushes the piston 6 outwards in the cylinder 45 against the resistance of a spring 48. The chamber I2 is dispensed with and the connection from the master cylinder 2 is to a chamber 49 into which the piston rod ii extends through a gland 50. The opposite end of the chamber is sealed by a packing element 5| disposed adjacent the inner end of the cylinder 25. From the chamber 49 a passage 52 leads to the cylinder 26 wherein a plunger 27 is arranged as in Figs. 1 and 2 to move a lever 29 about a pivot 30 to actuate the diaphragm valve arrangement omitted from Fig. 3 as being outside the plane in which the section is taken.

The arrangements according to the invention possess the advantage that failure of the vacuum source does not affect the hydraulic system as the hydraulic fluid is contained in sealed circuit which alone is capable of transmitting pulses through the column of liquid in conduit cylinder extension 9 and conduit 5 to the brake applying cylinders when the pedal i is actuated.

The invention possesses the further advantage in that the operating cylinder 13, the vacuum valve mechanism carried in and upon t; casing and the vacuum cylinder 25 together iorzn a self contained unit capable of installation at any con venient point on a va chassis es not require any mechanical assistance from chassis apart from more support.

I claim:

A servo-assisted operating mechanism, comprising a hydraulic cylinder havin means at its forward end for connecting it to at least one output cylinder, a valve casing secured to the rear end of the hydraulic cylinder and having a cylindrical chamber therein at the rear end of the hydraulic cylinder, a vacuum cylinder secured at one end to the valve casing in axial alignment with the hydraulic cylinder, a manually operable master cylinder communicating with said cylindrical chamber, a valved piston movably mounted within the hydraulic cylinder and having a central opening therein through which the master cylinder normally communicates with the output cylinder and a coned valve seat surrounding said opening, a spring opposing forward movement of said valved piston, a piston disposed within the vacuum cylinder and having a piston rod rojecting into said cylindrical chamber, said piston rod having a coned end surface and being adapted, upon operation of said piston, to be advanced into the hydraulic cylinder by its initial movement to engage its coned end surface with the coned valve seat of the valved pi to close said opening therein and by its furth advance to impart movement to the valved piston and thereby boost the pressure of fluid in the hydraulic cylinder, a valve chamber in said valve casing having a first passage for communication between said valve chamber and a source of vacuum and having a second passage for communes tion between said valve chamber and the vacuum cylinder, 3, spring-loaded disc valve member arranged normally to close said first passage, a lever pivotally mounted upon said valve casing externally thereof and having a free end, a ilexible diaphragm peripherally secured to the walls of said valve chamber and exposed on one side to atmosphere, a cylindrical member secured centrally to said diaphragm and connected to the free end of said lever and formed with ports through which said second passage and the vacuum cylinder normally communicate with atmosphere, said valve casing having a cylindrical core which extends inwardly from the exterior thereof and communicates at its inner end with the master cylinder and said cylindrical chamber at the rear of the valved piston, a plunger slidably mounted in said cylindrical bore, said plunger projecting outwardly beyond the outer end of said bore to bear against said lever intermediately of the ends thereof and being subjected at its inner end to the pressure of fluid in the master cylinder, and being operable, upon an increase in said fluid pressure, to actuate said lever to move said cylindrical member initially into engagement with the disc valve member to cut off the vacuum cylinder from atmosphere and subsequently by further movement of said cylindrical member to unseat said disc valve member and thereby place the vacuum cylinder in communication with the source of vacuum to eflfect operation of the piston therein.

STANLEY HOWARD EDGE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,393,524 Fant Jan. 22, 1946 2,446,884 Price Aug. 10, 1948 2,526,236 Ingres Oct. 17, 1950 2,536,461 Price Jan. 2, 1951 2,588,048 Rockwell Mar. 4, 1952 

